1. Field of the Invention
The present invention relates to a shaft sealing mechanism, a structure for mounting the shaft sealing mechanism on a stator, and a turbine including the shaft sealing mechanism and the structure for mounting the shaft sealing mechanism on a stator.
2. Description of the Related Art
In general, a turbine is provided around a rotor thereof with static blades and dynamic blades, and has a shaft sealing mechanism around the rotor in order to reduce a leakage amount of working fluid flowing from a high pressure side to a low pressure side. As one example of such a shaft sealing mechanism, there are leaf seals disclosed in Japanese Patent Application Laid-Open Nos. 2002-013647, 2003-113945, and the like.
The turbine includes a gas turbine and a steam turbine, and an entire structure of the gas turbine is shown, as one example, in FIG. 8. Air compressed by a compressor 1 is mixed with fuel to be combusted in a combustor 2. Combustion gas, as working fluid, generated in the combustor 2 expands so that thermal energy of the combustion gas is converted to rotational energy in the courses of passing through static blades 6 and dynamic blades 7, which are provided alternatively around a rotor 4. The thus converted rotational energy is taken out as electric power. A shaft sealing mechanism 11 is provided between each static blade 6 and the rotor 4 in order to reduce a leakage amount of the combustion gas from a high pressure side to a low pressure side, and a leaf seal is used as an example of the shaft sealing mechanism.
One example of a conventional shaft sealing mechanism including the leaf seals is shown in FIG. 9. The shaft sealing mechanism 11 has a structure in which many thin plates 121, having a fixed width in an axial line direction of the rotor 4, are arranged in a multi-layered manner. The shaft sealing mechanism 11 includes a thin plate group 12 where the thin plates are arranged annularly in a circumferential direction of the rotor 4 and are disposed with fine spacing along the circumferential direction thereof. The thin plate group 12 is joined at an outer peripheral proximal end 122 thereof, and an inner peripheral free end 123 thereof comes in sliding contact with a rotor outer peripheral face 4a to form an acute angle to the rotor 4 without being joined. Thus, an annular space 8, which is provided between the rotor 4 and a stator 5 to allow working fluid to flow, is partitioned into a high-pressure region and a low-pressure region.
The thin plate group 12 is fixed to a leaf seal ring 14 obtained by combining a pair of divided seal rings 14a and 14b, and each thin plate 121 has a T-shape cross section, including a rotor axial line. The leaf seal ring 14 also includes a high-pressure-side plate 15 provided on a side adjacent to the high-pressure region through the thin plate group 12, and a low-pressure-side plate 16 provided on a side adjacent to the low-pressure region as guide plates for working fluid. A length of the low-pressure-side plate 16 is shorter than that of the high-pressure-side plate 15 in a sectional view including the rotor axial line, in order to generate a floating force by a gas pressure distribution acting on upper and lower faces of the thin plates 121. Therefore, a gap defined between a stator inner wall 5a adjacent to the low-pressure region and a thin plate edge 125 (hereinafter, “low-pressure gap Y1”) is larger than a gap defined between the high-pressure-side plate 15 provided adjacent to the high-pressure region and a thin plate edge 124 (hereinafter, “high-pressure gap X”) (X<Y1).
The shaft sealing mechanism 11 with the above configuration is fittingly inserted into a recessed groove 31 provided on the stator 5. The inner peripheral free end 123 of each thin plate 121 is floated from the outer peripheral face 4a of the rotor 4 by a floating force due to working fluid acting on the thin plate 121 and a dynamic pressure effect of working fluid due to rotation of the rotor 4 to achieve a non-contacting state between the inner peripheral free end 123 and the outer peripheral face 4a. Thus, each thin plate is prevented from wearing and generating heat.
Conventionally, the shaft sealing mechanism with such a leaf seal has a divided portion in a radial direction to the rotor axial center in order to facilitate assembling. A plurality of pieces of the divided leaf seal are sequentially assembled to the stator to integrally exhibit a sealing function. However, even if the assembled and integrated annular seal is formed, since it has at least one (usually, plural) divided portion in a radial direction to the rotor axial center, high pressure working fluid eventually flows into the leaf seal via a gap formed by the divided portions. FIG. 10 schematically depicts a flow of working fluid around the divided portion of the leaf seal. An actual leaf seal has a head of the thin plate 121 formed in a wide T-shape in cross section, including the rotor axial center, but it is schematically simplified as a rectangular shape in FIG. 10. Working fluid that has flowed in the shaft sealing mechanism 11 from a divided portion 19 flows into the inside from a gap (a high-pressure gap) between the high-pressure-side plate 15 and the thin plate edge 124 of the thin plate 121 along the high-pressure-side plate 16 in a circumferential direction, to flow down on a surface of the thin plate 121 along upper and lower faces of the thin plate 121. As disclosed in Japanese Patent Application Laid-Open No. 2002-013647, the working fluid passes through a gap between the lower end of the high-pressure-side plate 15 and the rotor outer peripheral face 4a at any point in the circumferential direction on the leaf seal, except for around the divided portion of the leaf seal, to flow on the upper and the lower faces of the thin plate 121 from the side of the inner peripheral free end 123 of the thin plate 121 toward the side of the outer peripheral proximal end 122.
Around the divided portion, however, the working fluid flows from the divided portion 19 into the shaft sealing mechanism 11 while maintaining the same pressure over the entire length of the high-pressure-side plate 15 in a sectional view including the rotor axial line. Therefore, the same pressure acts on the side of the outer peripheral proximal end 122 and the side of the inner peripheral free end 123 around the thin plate edge 124 of the thin plate 121. This technique is different from the conventional example in this point. However, a pressing force acts on the thin plate due to fluctuation over a gas pressure distribution, and the inner peripheral free end 123 comes in contact with the rotor outer-surface 4a so that wearing and heat generation of the thin plate occurs.